I am using Auth0-lock UI for login user, but I am using Auth0-js to refresh the token. I am migrating from Auth0-js V7 (which uses refreshToken method) to Auth0-jv V8 (8.10.1) (which now uses checkSession).

Auth0-lock is also being upgraded from 10.8.1 (which uses v7) to 10.23.1 (which uses v8).
The Auth0-lock works fine for login.

Problem:

In the past, the refreshToken always worked fine, but with V8, whenever I call checkSession, I get an error (after a long time):

const storedRefreshToken = localStorage.getItem('refresh_token'); // I manually saved the refreshToken earlier after lock login success. According to V8 checkSession's documentation, I no longer have to do this.

I could not reproduce this situation and the checkSession either returned refreshed tokens or a login_required error if there was no session. If you can reproduce this consistently you should check the HTTP request/response for the call to /authorize that is performed when you invoke the checkSession method; ideally, you should include in your question data for that HTTP request and response pair (you can redact information you deem sensitive).

Thanks for the response. So does it mean anything when it says timeout during fetching SSO? (Is it because Auth0 Lock isn’t compatible with hosted page?)
For now, I decided to push out the migration until absolutely necessary, given the issues.

The timeout means something completely unexpected happened; for example, if you’re sending a completely wrong redirect URI or client identifier in the check session. My recommendation would be for you to review what was wrong and continue the migration.